ارزيابي آسيب در اتصالات قاب خمشي به كمك تبديل هيلبرت- هوآنگ

Damage Assessment in Connections of Moment Resistant Frames Using Hilbert-Huang Transform

گذشت زمان و بارهاي تصادفي از مواردي هستند كه سلامت سازه را مورد تهديد قرار مي دهند. تشخيص آسيب احتمالي سازه، نقش مهمي در كاهش ميزان خسارت‌هاي اقتصادي و اجتماعي ايفا مي‌كند. در اين نوشتار، روشي براي تعيين موقعيت و شدت آسيب به‌وجودآمده در اتصالات قاب هاي خمشي با بهره گيري از ويژگي هاي مودال سازه ارايه شده است. در اين روش با استفاده از پردازش شتاب پاسخ ارتعاش آزاد سازه به كمك تبديل هيلبرت- هوآنگ، بسامد هاي طبيعي و شكل هاي مودي سازه تخمين زده شده و با مقايسه‌ي انحنا شكل هاي مودي محاسباتي در وضعيت هاي مختلف سازه، اقدام به شناسايي آسيب در سازه شده است. صحت روش ارايه‌شده بر روي يك قاب خمشي 7 طبقه ي بتني و يك قاب خمشي 5 طبقه ي فولادي مورد بررسي قرار گرفته و نتايج نشان داده است كه با توجه به استفاده از تعداد معدودي از مودهاي سازه، روش ارايه‌شده بسيار كارآمد است و بنابراين در پايش سلامت سازه هاي واقعي موثر خواهد بود.

Environmental conditions and uncertainty in materials and service loads cause operational defects in structures. Detection of damage at the earliest stages can increase the life expectancy of structures and also prevent occurrence of disaster. So, structural health monitoring has been of interest over the last decades. Among the various methods for damage detection, vibrating response processing is one of the best and most efficient methods. Structural health monitoring systems are set up in such a way that the natural and forced vibrations can be investigated. So, by using reliable monitoring systems, structural behavior can be controlled in various stages of construction or operation. Occurrence of damage in a structure causes changes in its dynamic characteristics, such as its natural frequencies and mode shapes. Comparison of frequencies and mode shapes or mode shape curvature under various conditions can be used for health monitoring. For minor damage situations, direct comparison of modal parameters is not very useful. Instead, evaluation of mode shape curvature can be considered. In this paper, in order to detect damage in the connections of a moment resistant frame, a method based on analysis of the free vibration response of a frame, using Hilbert-Huang transform, is presented. In this methodology, natural frequencies and mode shapes of the frame are predicted by processing the acceleration response of the structure. Variation of the mode shape curvature is considered as damage index. This method is tested on the numerical model of a 2D concrete frame and a 3D steel frame as a benchmark. Different damage scenarios, such as single and multiple defects of beam-to-column connections, are investigated. Results show that the presented method is reliable for operation monitoring of connections in moment resistant frames by considering the low number of mode shapes, and its high accuracy in damage detection.